Syntheses And Properties Of ERI And MTW Zeotype Materials

Molecular sieves are a class of inorganic microporous crystalline materials that are widely used in petroleum refining and fine chemicals.In recent years,with the increasing seriousness of environmental pollution,molecular sieves with the potential applications in solving environmental pollution have gradually attracted the attention of scientists.Global warming caused by CO₂ emissions from fossil fuel combustion is a current worldwide problem.Molecular sieves with porous structures and active sites have demonstrated promising applications in CO₂ adsorption/separation and catalytic conversion.In addition to CO₂,NH₃ as the only alkaline gas in the atmosphere,is very easy to react with atmospheric SO₂ and NO_X to form secondary inorganic aerosol,which is one of the main culprits of haze.At present,the resistive NH₃ gas sensors in the real-time detection of NH₃ mainly use semiconductor oxides or organic semiconductors as sensitive materials,which suffer from poor selectivity and poor hydrothermal stability.Compared with transitional semiconductor gas-sensing materials,molecular sieves display advantages of high adsorption capacity,adjustable variable acidity,high temperature stability,hydrophobicity,catalytic activity,and higher mobility of metal cations in channels.Zeolite-sensing materials are expected to achieve highly sensitive and stable detection of ammonia gas.In this thesis,a series of MTW and ERI（SAPO-17）zeotype materials were synthesized by conventional hydrothermal method and microwave-assisted hydrothermal method,respectively.The effects of synthesitic method,crystallization method and crystallization temperature on the syntheses of MTW and ERI zeotype materials were investigated in detail.Besides,their catalytic activities in the cycloaddition reactions of CO₂ and styrene oxide as well as their performance in gas separation and detection were studied.The main research results were obtained as follows:1.By using N,N,N’,N’-tetramethyl-1,6-hexanediamine as an organic structure directing agent,SAPO-17 was rapidly prepared by microwave-assisted hydrothermal method with seeds or not.Then,the effect of the crystallization conditions of SAPO-17was investigated.The nanoscale SAPO-17-seed-1 was synthesized rapidly within 1 min by introducing crystalline seeds.The study showed that SAPO-17-seed-1 has higher adsorption enthalpy,so it shows excellent performance in CO₂/N₂ adsorption separation（CO₂/N₂ separation ratio reached 584）.This work provides a research basis for the efficient and green synthesis of nanosized molecular sieves and their application in the separation of CO₂/N₂.2.A series of MO/MTW catalysts were prepared by using tetraethylammonium hydroxide as an organic structure directing agent.Different metal oxides were loaded on the aluminosilicate molecular sieve MTW by simple incipient wetness impregnation method.The catalytic performance of MO/MTW catalysts in the cycloaddition reaction of CO₂ and styrene oxide was systematically investigated by varying the catalytic conditions（reaction temperature,reaction time and the type of metal oxides,etc.）.The strong acid sites of MTW molecular sieve can be reduced to achieve high selectivity of cyclic carbonate and high conversion of styrene oxide by increasing the basic sites via the simple impregnation method.3.By using tetraethylammonium hydroxide as an organic structure directing agent,Na-MTW molecular sieves with different Si/Al molar ratios have been successfully prepared in a concentrated gel system by seed-assisted route.High-performance ammonia sensors were constructed with Na-MTW molecular sieves,and the effect of Si/Al molar ratios on ammonia sensing was investigated.This work demonstrates that the decrease of the Si/Al ratio of Na-MTW zeolite is beneficial for increasing the ion conductivity of zeolite used as sensing material,and decreasing the baseline resistance in air of gas sensor based on Na-MTW zeolite.More importantly,this work can provide an innorative application route and research idea of zeolite-based ammonia gas sensor.